JPH0882633A - Near field microscope - Google Patents

Abstract

PURPOSE: To increase a degree of freedom of measurement by a method wherein a light from a light source is introduced by a plate-shaped waveguide existing on a specimen table to emit on an object to be observed via an opening on an under face of a tip thereof and relative positions of the waveguide and a photodetector with respect to the specimen table is varied by means of a scanning mechanism. CONSTITUTION: A waveguide 15 is placed above a specimen table 2 by being inclined and the upper end section thereof is supported by a scanning mechanism 16 that is constituted of an assembly of piezoelectric elements and is capable of controlling the movement of the waveguide in the triaxial directions with respect to the specimen table 2. The piezoelectric elements scan the waveguide 15 with the accuracy of nm in accordance with voltages. End faces of a core 15a and a clad 15b are exposed in an upper end section of the waveguide 15 and a laser light 3 from a light source 5 is incident thereto via a lens 20. The light 3 passes through the core 15b and a part thereof emits on an object 1 to be observed via an opening 9 in an under face of the other end section as an evanescent light 3a. An intensity of the reflection light 3c on the surface is measured by means of a photodetector 4. In the above constitution, it is possible to freely set a position and a shape of the opening 9 so that the incident angle to the object 1 to be observed can be freely set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a general-purpose and high-resolution optical microscope, and more particularly to a near-field microscope.

[0002]

2. Description of the Related Art In an ordinary optical microscope, the spatial resolution is limited by the diffraction limit of light, and the resolution is generally given by (wavelength of light) / (numerical aperture of lens), and is on the order of wavelength (λ). It is well known that there is. A near-field microscope is available as a means for overcoming this limitation.

A conventional near-field microscope has a light transmission type structure as shown in FIG. FIG. 5 is a schematic view showing a main part of the near-field microscope. As shown in the figure, the observed object 1 has a structure to be mounted on the sample table 2. Below the sample table 2, a photodetector 4 for detecting the transmitted light 3b transmitted through the observed object 1 and the sample table 2 is arranged. An optical fiber 6 for guiding the light 3 emitted from the light source 5 to the observed object 1 is arranged above the sample table 2. The optical fiber 6 is supported by an arm 7 of a scanning mechanism that changes the relative positional relationship between the optical fiber 6 and the observed object 1. The tip of the optical fiber 6 facing the sample table 2 is sharpened, and is covered with a coating 8 made of metal that covers the sharpened portion excluding the tip.

The tip portion of the optical fiber 6 which is not covered with the covering 8 forms an opening 9, which has a diameter not larger than the central wavelength (λ) of the light source 5. As a result, the light 3 is emitted from the opening 9 to the observed object 1.

The distance (a) between the object 1 to be observed and the aperture 9 is set to be equal to or less than λ so as to obtain a near field image.

In such a near-field microscope, the light 3 emitted from the light source 5 is guided (guided) to the optical fiber 6 and emitted from the opening 9 as the evanescent light 3a to the observed object 1. In the photodetector 4, the transmitted light 3b modulated by the optical properties of the observed object 1
Detect the light intensity of.

Since the optical fiber 6 supported by the arm 7 by the scanning mechanism is two-dimensionally scanned with respect to the observed object 1, a two-dimensional image of the observed object 1 (proximity A visual field image) is obtained.

In the near-field microscope, the resolution is almost equal to the diameter of the aperture 9, so that the resolution that can overcome the diffraction limit can be obtained, and thus has been attracting attention in recent years. In this example, the minute aperture is used as the light source, but the configuration of the minute photodetector in which the photodetector 4 below the sample table 2 is the light source and the light source 5 connected to the optical fiber 6 is the photodetector is also the same. Is known to have an effect. For these technologies,
Science, (1992), Vol.257, p189.

On the other hand, an atomic force microscope is known as a technique for observing the surface of an object to be observed. For example, the Institute of Electronics, Information and Communication Engineers Technical Report, Vol.
93 No.327, p31 to p36 describes a technique for observing a semiconductor surface in a solution by an atomic force microscope.

As a distance measuring technique for a moving object, the moving object is moved by irradiating the moving object with laser light and detecting the position of the laser spot of the reflected light with a position detecting element (two-division photodiode). A distance measuring method called "optical lever method" for detecting distance is J. Vac. Sci. (1990), Vol. A8.
(4), p3386. According to this "optical lever method", distance measurement can be performed with an accuracy of nm or less.

[0011]

The conventional near-field microscope as described above has the following problems. The tip of the optical fiber is sharpened depending on whether the optical fiber is stretched or chemically etched. However, in these methods, the controllability of the tip shape formation is poor, the degree of freedom of the obtained shape is low, and in principle, Only axisymmetric ones can be obtained. Due to the geometrical constraint that the optical fiber is a cylindrical body, the central axis of the optical fiber can only take a direction close to perpendicular to the surface of the observed object, and the incident angle cannot be changed greatly. It was That is, in the conventional near-field microscope, the observed object needs to be transparent because it can only be arranged to detect the transmitted light of the observed object, and thus it has poor versatility.

Further, it is necessary to precisely control the distance between the optical fiber and the object to be observed to be λ or less, but the one that is currently proposed is due to the tunnel current. But,
In the case of the tunnel current, the object to be observed must be a conductor, and there are many nonconductors such as a dielectric or a living body for optical observation, which is not suitable for controlling a near-field microscope.

Therefore, there is an attempt to utilize the atomic force acting between the object to be observed and the optical fiber. However, in order to measure the deflection of the optical fiber due to the atomic force, the optical fiber must be bent. Bending loss occurs and the SN ratio is further deteriorated, which is not practical.

An object of the present invention is to provide a near field microscope capable of increasing the degree of freedom of measurement of the near field microscope.

Another object of the present invention is to provide a near-field microscope having a high SN ratio, which can control the distance between the surface of the object to be observed and the opening for emitting the evanescent light by utilizing the atomic force. is there.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0017]

The outline of the representative ones of the inventions disclosed in the present application will be briefly described as follows. That is, the near-field microscope of the present invention includes a sample table on which an object to be observed is placed, and an object to be observed from an opening on the lower surface side of the tip that extends obliquely above the sample table and guides light from a light source. A waveguide that emits light, a photodetector that detects the intensity of light from the object to be observed, and a sample stage that measures the light intensity of the waveguide and the photodetector. A scanning mechanism for changing the relative positional relationship of the means, and a distance measuring mechanism for measuring the moving distance of the waveguide to detect the distance between the object to be observed and the opening, and the opening diameter of the opening. Is formed to be equal to or less than the wavelength of the light, and the distance between the object to be observed and the opening is set to be equal to or less than the wavelength of the light. Also,
The waveguide is a plate-shaped waveguide and an optical waveguide is provided.

A near field microscope according to another embodiment of the present invention comprises means for applying an electric field between the waveguide and the object to be observed, and means for measuring a tunnel current flowing between the waveguide and the object to be observed. It has a structure having.

A near-field microscope according to another embodiment of the present invention has a structure having means for measuring the atomic force acting between the waveguide and the object to be observed.

[0020]

According to the above-mentioned means, the near-field microscope of the present invention has a structure in which an opening is partially formed on the lower surface of the tip of a plate-shaped waveguide, so that the shape of the opening can be freely set. Can be set.

Further, in the near-field microscope of the present invention, the waveguide has an inclined cantilever structure, and
Since the position degree can be freely set by the scanning mechanism,
It is possible to obtain a free incident angle with respect to the observed object.

Further, in the near-field microscope of the present invention, the waveguide has an inclined cantilever structure, and
Even if the position of the waveguide is controlled by the scanning mechanism, the waveguide is not deformed and the signal strength is not lost.

In the near-field microscope of the present invention, since the incident angle can be freely set with respect to the object to be observed as described above, light can be reflected in addition to being transmitted to the object to be observed. Objects other than transparent objects can be observed.

Further, the near-field microscope of the present invention can control the distance between the object to be observed and the aperture on the order of nm by the optical lever method, and can obtain a stable near-field image. In the optical lever method, the displacement of the waveguide is measured,
If the spring constant of the cantilever is k and the displacement is d, the atomic force F acting on the cantilever and the object to be observed can be obtained using the relationship of F≈kd. By scanning while controlling so that the interatomic force between the waveguide and the object to be observed becomes constant, a concavo-convex image of the object to be observed can also be obtained at the same time.

A near-field microscope according to another embodiment of the present invention comprises means for applying an electric field between the waveguide and the object to be observed, and means for measuring a tunnel current flowing between the waveguide and the object to be observed. Therefore, by controlling the intensity of the tunnel current to be constant, the distance between the waveguide and the object to be observed can be controlled in the nm order, and the unevenness image of the object to be observed can also be obtained from the control signal. Also obtained.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a main part of a near-field microscope according to an embodiment of the present invention. In all the drawings for explaining the embodiments, the same reference numerals are given to those having the same functions, and the repeated description thereof will be omitted.

The near-field microscope of the present invention comprises an object 1 to be observed.
It has a structure for detecting the reflected light reflected on the surface of the. In the figure, 2 is a sample table on which the observed object 1 is placed on the upper surface (main surface). The observed object 1 is a conductor, a nonconductor, a part of a living body, or the like.

A flat plate-shaped waveguide 15 extending obliquely extends above the sample table 2. The upper end portion of the waveguide 15, that is, the right end portion in the figure, is supported by a scanning mechanism 16 capable of movement control in three axial directions with respect to the sample table 2. The scanning mechanism 16 is a scanning mechanism that incorporates a piezo element, and nm in the plane (XY direction) direction along the surface of the sample table 2 and in the Z direction approaching and separating.
Movement control is possible on the order. Scanning mechanism 16
Has the following specific structure. The scanning mechanism has, for example, as shown in FIG. 3, a structure in which three piezo elements 16a, 16b, and 16c are combined in the XYZ directions, and a power supply for driving the piezo elements. The piezo element is a waveguide 15 with voltage accuracy of nm.
Can be scanned.

The waveguide 15 is made of SiO 2 having a thickness of about 1 μm.
A core 15a made of N and SiO2 having a thickness of about 0.45 .mu.m provided so as to cover the upper surface of the surface of the core 15a.
And a clad 15b made of a film. Further, the lower end portion of the waveguide 15, that is, the left end portion in the figure, is
A metal film 17 made of aluminum or the like having a thickness of about 50 nm is provided so as not to transmit light. Further, a part of the lower surface of the tip of the waveguide 15 is partially polished by the focused ion beam treatment, and as shown in FIG.
5, the core 15a is partially exposed on the lower surface of the tip of
There is provided an opening 9 for emitting the light to the observed object 1. The core 15a forms a waveguide for guiding light.

On the other hand, the upper end of the waveguide 15 has a core 15
The end faces of a and the clad 15b are exposed. The light 3 emitted from the light source 5 made of laser light is focused on the end surface of the core 15a via the coupling lens 20. The light 3 incident on the inside of the core 15a from the end of the core 15a passes through the waveguide formed by the core 15a, and a part of the light 3 is emitted from the opening 9 to the surface of the observed object 1. The opening 9 is set to a wavelength (λ) of the light source 5 or less. As a result, the evanescent light 3a that is abruptly attenuated spatially on the order of the opening diameter is emitted from the opening 9.

Since the waveguide 15 is inclined and is controlled by the scanning mechanism 16, the incident angle of the evanescent light 3a is controlled by controlling the waveguide 15 by the scanning mechanism 16. It can be at any desired angle.

The evanescent light 3a is reflected on the surface of the object 1 to be observed, and a part of the reflected light 3c reaches a photodetector (light intensity measuring device) 4, as shown in FIG. The light intensity will be measured.

In the near-field microscope, the observed object 1
The distance (a) between the aperture 9 and the aperture 9 is set to be equal to or less than λ so as to obtain a near-field image. Therefore, the accuracy of the distance measuring mechanism of the waveguide 15 is required to be as high as nm. Therefore, in this embodiment, the optical lever method is adopted. That is, the flat surface of the waveguide 15 is irradiated with the laser light 31 emitted from the laser light source 30, and the reflected light 32 is detected by the position detecting element 33. The position detecting element 33 is not particularly limited, but a two-divided photodiode is used. This makes it possible to detect a change in the distance between the object 1 to be observed and the aperture 9 on the order of nm.

Incidentally, the light source 5 and the coupling lens 20.
The light source optical system including the above is integrally connected to the waveguide 15. Further, each part constituting the optical lever method and the photodetector 4 also have a linkage structure which maintains a constant relationship with the scanning mechanism 16.

From the above, the relative position of the means for measuring the light intensity, which is composed of the waveguide 15 and the light intensity measuring device, is freely changed with respect to the sample stage 2 by the scanning mechanism 16. be able to.

In such a near-field microscope, a near-field image is obtained while setting the distance between the object to be observed 1 and the opening 9 to be the wavelength of the light 3 or less.

According to such a near field microscope, the following effects can be obtained.

(1) Since the near-field microscope of the present invention has a structure in which an opening is partially formed on the lower surface of the tip of a plate-shaped waveguide, the tip of a conventional cylindrical optical fiber is Compared to the sharpened opening, the position and shape of the opening can be freely set.

(2) In the near field microscope of the present invention, the waveguide has an inclined cantilever structure, and
Since the position degree can be freely controlled by the scanning mechanism,
The effect that a free incident angle can be obtained with respect to the observed object is obtained.

(3) In the near field microscope of the present invention, the waveguide has an inclined cantilever structure, and
Even if the position of the waveguide is controlled by the scanning mechanism, the waveguide is not deformed, and the effect of preventing the loss of signal strength can be obtained.

(4) Since the near-field microscope of the present invention can set a free incident angle to the object to be observed as described above, it can reflect light in addition to transmitting it to the object to be observed. The object to be observed may be something other than a transparent body, and the effect of becoming versatile is obtained.

(5) In the near-field microscope of the present invention, the distance between the object to be observed and the aperture can be controlled on the order of nm by the optical lever method, so that a stable near-field image can be obtained.

(6) The near-field microscope of the present invention can obtain an atomic force image simultaneously with a near-field image by measuring the atomic force acting on the waveguide and the object to be observed by the optical lever method. The effect of being able to detect the surface state of the observed object with higher accuracy can be obtained by comparing the two.

As described above, the invention made by the present inventor is
Although the present invention has been specifically described based on the above-mentioned embodiments, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the scope of the invention.

For example, in FIG. 4, means (voltage applying means 41) for applying an electric field between the waveguide 15 and the object to be observed 1 without using the optical lever method, the waveguide 15 and the object to be observed. It is configured to have a means (ammeter 42) for measuring a tunnel current flowing between the objects 1, and it is possible to precisely control the distance between the waveguide 15 and the object 1 to be observed and obtain an uneven image of the object to be observed. Has the effect of saying.

In each of the above-mentioned embodiments according to the present invention, the structure in which light is reflected on the surface of the object to be observed has been described. However, the intensity of light transmitted through the object to be observed is detected to obtain a near-field image. Of course, it can be applied to the structure for obtaining.

[0047]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows. The near-field microscope of the present invention uses a flat waveguide as a probe for guiding light that faces an object to be observed,
And because it has a cantilever structure that extends diagonally,
The incident angle of light with respect to the observed object can be freely set, and a desired near-field image can be obtained.

Further, since the near-field microscope of the present invention detects the reflected light to detect the surface of the object to be observed, a substance that does not transmit light can be used as the object to be observed, and is excellent in versatility. Will be things.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a main part of a near-field microscope according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a main part of a waveguide in the near-field microscope according to the present embodiment.

FIG. 3 is a schematic view showing a main part of a scanning mechanism according to this embodiment.

FIG. 4 is a schematic view showing a main part of a near-field microscope according to another embodiment of the present invention.

FIG. 5 is a schematic diagram showing a main part of a conventional near-field microscope.

[Explanation of symbols]

1 ... Observed object, 2 ... Sample stage, 3 ... Light, 3a ... Evanescent light, 3b ... Transmitted light, 4 ... Photodetector, 5 ... Light source, 6
... optical fiber, 7 ... arm, 8 ... coating, 9 ... aperture, 1
5 ... Waveguide, 15a ... Core, 15b ... Clad, 16 ...
Scanning mechanism, 16a, 16b, 16c ... Piezo element, 17
... metal film, 20 ... coupling lens, 30 ... laser light source, 3
1 ... Laser light, 32 ... Reflected light, 33 ... Position detection element.

Claims (4)

[Claims] 1. A sample table on which an object to be observed is placed, and a sample table that extends obliquely above the sample table and guides light from a light source and emits the light to the object to be observed from an opening on the lower surface side. A waveguide, a photodetector for detecting the intensity of light from the object to be observed, and a means for measuring the light intensity of the waveguide and the photodetector relative to the sample stage. It has a scanning mechanism that changes the positional relationship and a distance measuring mechanism that measures the moving distance of the waveguide to detect the distance between the object to be observed and the opening, and the opening diameter of the opening is the wavelength of the light. A near-field microscope, which is formed below and is configured such that a distance between the object to be observed and the opening is set to be equal to or less than the wavelength of the light. 2. The near-field microscope according to claim 1, wherein the waveguide is a plate-shaped waveguide and an optical waveguide is provided. 3. The apparatus according to claim 1, further comprising means for applying an electric field between the waveguide and the object to be observed, and means for measuring a tunnel current flowing between the waveguide and the object to be observed. Near-field microscope. 4. The near-field microscope according to claim 1, further comprising means for measuring an interatomic force acting between the waveguide and the object to be observed.